Process for the production of carbonaceous tapes

ABSTRACT

An improved process is provided for the simultaneous conversion of a plurality of adjoining parallel ends of an organic polymeric fibrous material to a carbonaceous fibrous material. The parallel warp ends are provided and maintained during at least a portion of the conversion process an an integral tape possessing a high degree of structural integrity by the presence of a weft pick interlaced therewith in a sateen weave construction which floats a substantial number of the parallel warp ends as described. When the resulting carbonaceous tape is incorporated in a matrix material to form a composite article, the presence of the weft pick therein produces no substantial diminution in the composite properties.

Burns et al.

PROCESS FOR THE PRODUCTION OF CARBONACEOUS TAPES Assignee:

Filed:

Appl. No.: 112,189

Inventors: Kenneth S. Burns, Basking Ridge;

George R. Ferment, Dover, both of N.J.; Roger C. Waugh, Rock Mart, Ga.

Celanese Corporation, New York, NY.

Feb. 3, 1971 US. Cl 264/29, 264/DIG. 19, 423/447,

References Cited UNITED STATES PATENTS 1 June 18, 1974 3,424,133 12/1969Dickson et a1, 264/29 3,528,774 9/1970 Ezekiel et a1. 264/29 3,529,9349/1970 siiiiido. 8/116 R 3,656,910 4/1972 Ferment 23/2091 3,669,1586/1972 Phillips 139/420 Primary Examiner-Henry S. Jaudon 5 ABSTRACT Animproved process is provided for the simultaneous conversion of aplurality of adjoining parallel ends of an organic polymeric fibrousmaterial to a carbonaceous fibrous material. The parallel warp ends areprovided and maintained during at least a portion of the conversionprocess an an integral tape possessing a high degree of structuralintegrity by the presence of a weft pick interlaced therewith in asateen=weave construction which floats a substantial number of theparallel warp ends as, described. Whenthe' resulting carbonaceous tapeis incorporated in a'matrix material to form a composite article, thepresence of the weft pick therein produces no substantial diminution inthe,

composite properties.

13 Claims, 8 Drawing Figures if 1 1 1 1 i PATENTEBJUN 1 8 1914 'SHEEF20? a 8 8 8 8 1 1 1 1 7 7 7 7 1 1 1 1 6 6 6 6 1 11 1 5 5 5 5 1 1 11 4 44 4 11 1 1 3 33 3 1 11 1 2 2 2 2 1 1 11 S D 11 1 1 N 11 1 1 E 0 0 0 1 111 W 9 9 9 9 A W 8 8 8 8 7 7 7 7 6 6 6 6 5 5 5 4 4 4 4 3 3 3 3 2 2 2 2 11 1 1 8 7 6 5 4 3 2 1 2 TS F K r WD.

SELVAGE PORUON or- MMNEODY OF TAPE s D N E w A W PoRnoN OF MAN saw OFTAPE SELVAGE WARP ENDS 5 WK m W0.

m/veA/ro/es, KEA/A HH 5T Bum/5 650/265 Z fizz/ W F065? 6 M0616PATENTEUJUM m 51818082 SHEET 30F Q nvvavmres,

PROCESS FOR THE PRODUCTION OF CARBONACEOUS TAPES BACKGROUND OF THEINVENTION In the search for high performance materials, considerableinterest has been focused upon carbon fibers. The terms carbon fibers orcarbonaceous fibers are used herein the generic sense and includegraphite fibers as well as amorphous carbon fibers. Graphite fibers aredefined herein as fibers which consist essentially of carbon and have apredominant x-ray diffraction pattern characteristic of graphite.Amorphous carbon fibers, on the other hand, are defined as fibers inwhich the bulk of the fiber weight can be attributed to carbon and whichexhibit an essentially amorphous x-ray diffraction pattern. Graphitefibers generally have a higher Youngs modulus than do amorphous carbonfibers and in addition are more highly electrically and thermallyconductive.

Industrial high performance materials of the future are projected tomake substantial utilization of fiber reinforced composites, andgraphitic carbon fibers theoretically have among the best properties ofany fiber for use as high strength reinforcement. Among these desirableproperties are corrosion and high temperature resistance, low density,high tensile strength, and high modulus. Uses for carbon fiberreinforced composites include aerospace structural components, rocketmotor casings, deep-submergence vessels and ablative materials for heatshields on re-entry vehicles.

As is known in the art, numerous procedures have been proposed in thepast for the conversion of various organic polymeric fibrous materialsto a carbonaceous form while retaining the original fibrousconfiguration essentially intact. Such procedures have in common thethermal treatment of the fibrous precursor in an appropriate atmosphereor atmoshpheres which is commonly conducted in a plurality of heatingzones, or alternatively in a single heating zone wherein the fibrousmaterial is subjected-to progressively increasing tempera tures. Bothbatch and continuous processing techniques have been proposed. From thecommerical LII standpoint those processes which are capable of funcltioning on a continuous basis are generally considered to be the mostattractive. However, many of the prior art continuous conversiontechniques have been inherently limited to the processing of a singleend of fibrous precursor at a given time. Such techniques while offeringthe advantages of possible automation, still suffer the disadvantage oflimited productivity.

Additionally, techniques have been proposed wherein a plurality of endsof a fibrous precursor may be simultaneously processed. See for instantthe process of commonly assigned U.S. Ser. Nos. 865,332, filed Oct. 10,l969. of Kenneth S. Burns and William M. Cooper (now abandoned) whereina multiplicity of strands of polymeric fibrous material aresimultaneously stabilized prior to subsequent carbonization; and874,731, filed Nov. 7, 1969, (now US. Pat. No.

I 3,723,157), of Melvin L. Druin wherein a plurality of multifilamentbundles capable of undergoing graphitization are simultaneouslygraphitized and subsequently coated. While such generically definedprocesses offer substantial advantages over prior art batch andcontinuous processes, fiber handling difficulties may occasionallyarise. For example, if one of the fibrous ends undergoing treatmentshould be defective, the breakage of the same while being passed throughone of the heating zones frequently results in catastrophic failure ofthe process. The operation of the process must be terminated, the ovenor ovens cooled, and the broken end re-united or replaced. Also, precisehandling of the plurality of ends is essential if substantial endcrossovers are to be eliminated and a uniform width of the plurality ofthe ends maintained.

One technique heretofore proposed for the simultaneous conversion of asubstantial number of fibrous ends to a carbonaceous form has involvedthe thermal treatment of a fibrous precursor while in the form of awoven cloth. See, forinstance, Belgian Pat. Nos. 720,947 and 726,761, aswell as US. Pat. No. 3,541,582 for representative disclosures of theprocessing of cloth precursors. While fibrous assemblages in cloth formcommonly offer advantages with respect to the maintenance of structuralintegrity throughout the thermal treatment, a permanent crimp iscommonly imparted to the filaments and the single filament tensileproperties of the fibers present within the cloth have tended to beadversely influenced. Additionally a-high degree of fiber loading withina composite article is commonly impossible because of the inability ofthe cloth to form compact plys within the same. The weft threads in thecloth further appear to produce an overall reduction in the compositephysical properties.

It is an object of the invention to provide an improved process for thesimultaneous conversion of a plurality of adjoining ends of an organicpolymeric fibrous material while in the form of a tape to a carbonaceousfibrous material.

It is an object of the invention to provide an improved process for thesimultaneous conversion of a plurality of adjoining ends of an organicpolymeric fibrous material to a carbonaceous fibrous material while inthe form of a tape of enhanced structural integrity.

It is an object of the invention to provide an improved process for thesimultaneous conversion of a plurality of adjoining ends of an organicpolymeric fibrous material to a carbonaceous fibrous material whereincatastrophic process failure resulting from the breakage of an end iseffectively eliminated.

It is an object of the invention to provide an improved process for thesimultaneous conversion of a plurality of adjoining ends of an organicpolymeric fibrous material to a carbonaceous fibrous material while inthe form of a tape wherein splits and crossovers are substantiallyeliminated.

It is another object of the invention to provide an improved process forthe simultaneous conversion of a plurality of adjoining ends of anorganic polymeric fibrous material wherein the warp ends are maintainedin position by at least one weft pick in the substantial absence of theimpairment of the linear configuration and tensile properties of thewarp ends.

It is another object of the invention to provide an improved process forthe conversion of a plurality of adjoining ends of an organic polymericfibrous material to an integral carbonaceous tape which is capable of ahigh degree of compaction and fiber loading when utilized as areinforcing medium in a composite article.

lt is another object of the invention to provide an improved process forproducing a woven carbonaceous tape which when utilized as a reinforcingmedium yields a composite article of enhanced ties.

It is a further object of the invention to provide in a preferredembodiment an improved process for producing carbonaceous tapes from afibrous acrylic pre cursor.

These and other objects, as well as the scope, nature, and utilizationof the invention will be apparent from the detailed description whichfollows, and the appended claims.

SUMMARY OF THE INVENTION It has been found in a process for thesimultaneous conversion of a plurality of adjoining ends of an organicpolymeric fibrous material capable of undergoing conversion to acarbonaceous fibrous material while in the form of a tape to acarbonaceous fibrous material wherein the ends are continuously passedin the direction of their length through a series of heating zones whilesubstantially suspending therein to form a fibrous product whichcontains at least 90 per cent carbon by weight, that improved resultsare achieved by providing the fibrous material during at least a portionof the conversion process in the form of a tape of sateen weaveconstruction consisting of at least 32 adjoining substantially parallellinear warp ends capable of undergoing conversion to a carbonaceousfibrous material essentially coextensive with the length of the tape anda weft pick interlaced therewith at a plurality of points capable ofmaintaining the substantially parallel relationship of the warp endswhich substantially floats at least four of the warp ends prior to eachadditional interlacing point in the main body of the tape as the warpends are traversed, the weft pick being provided at a tension sufficientthat the linear configuration of the warp ends is substantiallyunimpaired and at a frequency of about 0.1 to 8 picks per inch of thetape.

The preferred organic polymeric fibrous material is an acrylic polymercomprising at least about 85 mol per cent of acrylonitrile units and upto about mol per cent of one or more monovinyl units copolymerizedtherewith. Ina preferred embodiment of the process the organic polymerictape is provided in the sateen weave construction throughout theconversion process.

physical proper- DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged planview ofa portion of precursor tape of a 4 X 4 sateen weave constructionsuitable for use in the present process. 7

FIG. 2 is the numerical weaving pattern for the tape of FIG. 1.

FIG. 3 is an enlarged plan view of a portion of precursor tape of an 8 X8 sateen weave construction suitable for use in the present process.

FIG. 4 is the numerical weaving pattern for the tape of FIG. 3.

FIG. 5 is an enlarged plan view of a portion of precursor tape of a 16 X16 sateen weave construction suitable for use in the present process.

FIG. 6 is the numerical weaving pattern for the tape 7 of FIG. 5.

FIG. 7 is an enlarged plan view of a portion of precursor tape having aweaveconstruction not in accordance with that employed in the presentprocess and is presented for comparative purposes.

F IG. 8 is the numerical weaving pattern for the tape of FIG. 7 and ispresented for comparative purposes only.

DESCRIPTION OF PREFERRED EMBODIMENTS The tape which is converted to acarbonaceous fi brous material possesses a sateen weave construction (asdescribed in detail hereafter) during at least a portion of theconversion process which includes at least 32 adjoining substantiallyparallel linear warp ends.

The warp ends are composed of an organic polymeric fibrous materialcapable of conversion to a carbonaceous fibrous material. The warp endsmay be conveniently selected from those fibrous materials which arerecognized as being suitable for thermal conversion to a carbonaceousfibrous material. For instance, the warp ends may be derived fromorganic polymers such as an acrylic polymer, a cellulosic polymer, apolyamide, a polybenzimidole, polyvinyl alcohoi, pitch, etc. Asdiscussed hereafter, acrylic polymeric materials are particularly suitedfor use in the formation of the warp ends employed in the presentprocess. Illustrative examples of suitable cellulosic materials includethe natural and regenerated forms of cellulose, e.g. rayon. Illusttativeexamples of suitable polyamide materials include the aromaticpolyamides, such as nylon 6T, which is formed by the condensation ofhexamethylenediamine and terephthalic acid. An illustrative example of asuitable polybenzimidazole is poly-2,2-mphenylene-5,5'-bibenzimidazole.

An acrylic polymeric material prior to thermal stabilization may beformed primarily of recurring acrylonitrile units. For instance, theacrylic polymer should contain not less than about mol per cent ofacrylonitrile units with not more than about 15 mol per cent ofmonovinyl compound which is copolymerizable with acrylonitrile such asstyrene, methyl acrylate, methyl methacrylate, vinyl acetate, vinylchloride vinylidene chloride, vinyl pyridine, and the like, or aplurality of such monomers. A particularly preferred acrylic polymericmaterial is an acrylonitrile homopolymer, or a closely relateacrylonitrile copolymer (Le. contains at least about mol per cent ofacrylonitrile units and up to about 5 mol per cent of one or moremonovinyl compouds copolymerized with acrylonitrile.

The warp ends may be provided in a variety of physical configurations.For instance, the warp ends may assume the configuration of continuouslengths of multifilament yarns, tows, strands, cables, or similarfibrous assemblages. In a preferred embodiment of the process the warpends are a continuous multifilament yarn.

The warp ends may optionally be provided with a twist which tends toimprove the handling characteristics. For instance, a twist of about 0.1to 5 tpi. and preferably about 0.3 to 1.0 tpi, may be utilized Also, afalse twist may be used instead of or in addition to a real twistAlternatively, one may select bundles of fibrous material which possessessentially no twist.

The warp ends may be drawn in accordance with conventional techniques inorder to improve their orientation. For instance, acrylic warp ends maybe pre- Iiminarily drawn by stretching before or after incorporaton inthe tape while in contact with a hot shoe at about to C. Additionalrepresentative drawing techniques are disclosed in U.S. Pat. Nos.2,455,173; 2,948,581; and 3,122,412. It is recommended that acrylic warpends selected for use in the process be initially drawn to a singlefilament tenacity of at least about 3 grams per denier. If desired,however, the warp ends may be more highly-oriented, e.g. drawn up to asingle filament tenacity of about 7.5 to 8 grams per denier, or more.

The weft pick is preferably also composed of an organic polymericfibrous material which is capable of undergoing carbonization withoutthe destruction of its original fibrous configuration. if desired,however, the weft pick may be initially provided as a previouslystabilized organic polymeric fibrous material, a carbonaceous fibrousmaterial, or other fibrous material capable of withstanding thecarbonization temperatures. A]- ternatively, a weft pick may be selectedwhich is incapable of withstanding the highly elevated temperaturesrequired to complete carbonization and/or graphitization of the warpends. For instance, the weft pick may be formed from a cellulosicmaterial such as cotton which will impart dimensional stability to thewarp ends through the stabilization step, but which is incapable ofwithstanding a subsequent heat treatment step.

The weft pick may be provided in a variety of physical configurations.For instance, the weft pick may assume the configuration of amultifilament yarn, tow, strand, cable, or similar fibrous assemblage.in a preferred embodiment of the process the weft pick is a continuousmultifilament yarn having a total denier equal to or less than that ofthe continuous multifilament yarn warp ends. Preferably the total denierof a multifilament acrylic yarn weft pick prior to thermal stabilizationis below about 400, e.g. about 100 to 300, total denier. In aparticularly preferred embodiment of the process the total denier of theweft pick is about 0.2 to 0.5 times the total denier of a warp end. Aminor amount of twist may be beneficially provided in a multifilamentyarn weft pick which improves the handling characteristics duringweaving. For instance, the weft pick may be provided with a twist ofabout 0.1 to 5 tpi (preferably 0.1 tov 3 tpi), and most preferably about0.2 to 0.7 tpi. if a twist is utilized in the warp ends it isrecommended that any twist employed in the weft pick be to a lessordegree so that the weft pick may readily assume a more flatenedconfiguration when in contact with warp ends.

it is essential that the weft pick utilized in the formation of the tapelacks a tendency to undergo excessive shrinkage during heat treatment(described hereafter) which imparts a pucker to the warp ends andthereby interferes with the flat configuration of the tape. in apreferred embodiment of the process the weft pick is hot drawn at leastabout 3 times itsas-spun length to .increase its orientation and issubsequently relaxed (e.g. 5 to 40 per cent of drawn length) prior toincorporation in the precursor tape so that its tendency to undergoshrinkage is minimized. 1

The fibrous material utilized as the warp ends and weft pick mayoptionally be provided in intimate association with one or morecatalytic agents capable of enhancing the rate of the thermal conversionto a carbonaceous fibrous material.

The fibrous organic polymeric tape utilized as the procursor in theprocess of the present invention during at least a portion of itsthermal conversion to a carbonized form is provided in a highlyunbalanced sateen weave construction. A sateen weave construction isdefined as a woven construction possessing a substantial number offloats which run fillingwise (i.e. weftwise). The tern float is used inits usual sense and indicates that a plurality .ofsubstantiallyperpendicular strands present within the construction are being passedover or skipped in the absence of interlacement. The tape is unbalancedin the sense that the numerical proportion of warp ends to filling picksper square inch present within the same is substantially greater than1:1, e.g. about 4:1 to 100:1, or more, and preferably about :1 to 30:1.The tape comprises at least 32 ad- 10 joining substantially parallellinear warp ends. Commonly, the tape comprises about 32 to 500 adjoiningwarp ends; however, even a substantially larger number of warp ends canbe employed, e.g. 1,000 or more. The warp ends are essentiallycoextensive with the length of the tape. The weft pick present withinthe tape of sateen weave construction is provided at a frequency ofabout 0.1 to 8 picks per inch of said tape, and preferably at afrequency of about 1 to 3-picks per inch of said tape. Since the weftpick is provided at a relatively low frequency, and preferably as acontinuous length, it

may intersect the edge of the tape at an angle other than exactly ninetydegrees unlike common woven fabrics. The exact angle of intersectionwith the edge of the tape is influenced by the pick frequency, and thewidth of the tape (i.e. number and total denier of the warp ends). I

The sateen weave construction of the tape is such that the weft pick isinterlaced with the warp ends at a plurality of points capable ofmaintaining the substantially parallel relationship of the warp endswhich are in an adjoining relationship in the form of a flat tape withcontact being made between contiguous warp ends. The weft pick isprovided under a tension sufficient that the linear configuration of thewarp ends present within the tape is substantially unimpaired.Additionally, any crimp which is present in the tape components shouldbe present in the weft pick and not in the warp ends.

The weft pick is interlaced with the warp ends insuch a manner that itsubstantially floats at least four of the warp ends prior to eachadditional interlacing point in the main body of the tape, i.e. thecentral portion of the tape with the possible exclusion of the selvage.More specifically, the weft pick floats from about four to 16, or more,of the warp ends prior to each additional interlacing point-in the mainbody of the tape as the warp ends are traversed. As the weft pick passesbetween adjoining warp ends in the main body of the tape at an interlacing point, an additional float preferably of like length is begunon the opposite face of the tape. Accordingly, floats of at least fourwarp ends are substantially present upon each face of the main tapebody. Such floats maintain the warp ends as an integral tape ofcontrolled lateral integrity. in the particularly preferred embodimentof the process the weft pick floats about eight of the warp ends priorto the next interlacing point. While standard weaving equipment iscommonly incapable of producing a sateen weave construction wherein morethan 16 warp ends are floated, this fact should not limit the maximumfloat utilized in the process to 16 warp ends. it should be recognized,however, that the structural integrity of the tape tends to be reducedif the float greatly exceeds 16 warp ends, e.g. up to about 50 warpends.

The lengths of the floats utilized in the sateen weave construction inthe main body of the tape need not be identical provided at least fourof the substantially parallel linear warp ends are skipped prior to eachadditional point of interlacement. It is preferred, however, that floatsof substantially uniform length (i.e. naturally balanced in weftdirection) be used throughout a given sateen weave construction. Suchsubstantially uniform float lengths aid in imparting transverse symmetryto the resulting tape which enhances its ability to maintain a flatconfiguration as the carbonization reaction progresses. The intersectionpoints are preferably varied between successive weft interlacements.Accordingly, as will be apparent to those skilled in weaving technology,the counter (i.e. step or move) of the sateen weave construction maycommonly be from about one to 10, or more, and is preferably one.

The tape of sateen weave construction utilized in the present processcan be formed by conventional weaving techniques as will be apparent tothose skilled in weaving technology. For instance, the warp ends may bebeamed, and the weft pick subsequently inserted at appropriate intervalsutilizing a narrow fabric loom. Care, of course, must be taken to insurethat the tension exerted upon the weft pick is insufficient to impairthe substantially linear configuration of the warp ends.

In a preferred embodiment of the process the tape of sateen weaveconstruction (as previously described) is provided with a selvage whichis capable of aiding the structural integrity of the weave. Such selvagemay be positioned upon each edge of the main body of the tape and is ofa relatively narrow width. For instance, the selvage may be formed byconverting the sateen weave construction created by the weft pick to aplain weave construction as the pair of warp ends at each edge of thetape are traversed. Such a selvage of relatively narrow width has beenfound helpful in retaining the weft pick at substantially the samelocation as initially woven, and does not deleteriously influencecomposite properties to any significant degree.

The heating temperatures, heating atmospheres, and residence timesutilized in the present process to produce carbon fibers may be inaccordance with thermal conversion techniques heretofore known in theart. The plurality of adjoining ends of an organic polymeric fibrousmaterial while in the form of a tape are converted to a carbonaceousfibrous material by continuous passage in the direction of their lengththrough a series of heating zones while substantially suspended thereinto form a fibrous product which contains at least 90 per cent carbon byweight'The organic polymeric fibrous tape during at least a portion ofits thermal conversion to a carbonaceous fibrous material is provided inthe form of a highly unbalanced tape of a sateen weave configuration (asheretofore described). in a preferred embodiment of the process theorganic polymeric fibroustape is provided in the sateen weaveconfiguration throughout its thermal conversion to a carbonaceousfibrous material. Alternatively, the sateen weave tape configuration maybe formed subsequent to an initial thermal stabilization treatment. Additionally, the sateen weave tape configuration may be optionallyretained while the tape is passed through any or all of the following(1) a graphitization zone, (2) a surface treatment zone wherein thesurface characteristics of the fibrous product are modified so as toenchance its bonding characteristics to a matrix material, and (3) aresin impregnation zone.

The stabilization heating zone is commonly provided at a temperature ofabout 200 to 400C. depending upon the composition of the tape. As willbe apparent to those skilled in the art, the atmosphere provided in thestabilization heating zone may be varied. For instance, a cellulosicprecursor is commonly stabilized in l an oxygen-containing atmosphere or(2) in an inert or non-oxidizing atmosphere, such as nitrogen, helium,argon, etc. Additionally, precursors such as an acrylic polymer, apolyamide, a polybenzimidazole, or polyvinyl alcohol are commonlystabilized in an oxygencontaining atmosphere. Air may be convenientlyselected as the oxygen-containing atmosphere for use in the process.When the stabilization treatment is conducted in an oxygen-containingatmosphere, it is commonly termed a preoxidation treatment.

The stabilization heating zone is substantially closed in order tofacilitate the confinement and withdrawal of off gases and/or themaintenance of an appropriate atmosphere. When a non-oxidizingatmosphere is desired within the heat treatment chamber, the strands maypass through a seal as they continuously enter and leave the heattreatment chamber in order to exclude oxygen.

The stabilization of fibers of acrylonitrile homopolymers and copolymersin an oxygen-containing atmosphere involves 1) an oxidativecross-linking reaction of adjoining molecules as well as (2) acyclization reaction of pendant nitrile groups to a condenseddihydropyridine structure. While the reaction mechanism is complex andnot readily explainable, it is believed that these two reactions occurconcurrently, or are to some extent competing reactions.

The cyclization reaction involving pendant nitrile groups which occursupon exposure of an acrylic fibrous material to heat is generally highlyexothermic and, if uncontrolled, results in the destruction of thefibrous configuration of the starting material. In some instances thisexothermic reaction will occur with explosive violence and result in thefibrous material being consumed by flame. More commonly, however, thefibrous material will simply rupture, disintegrate and/or coalesce whenthe critical temperature is reached. As the quantity of comonomerpresent in an acrylonitrile copolymer is increased, a fibrous materialconsisting of the same tends to soften at a progressively lowertemperature and the possible destruction of the original fibrousconfiguration through coalescence of adjoining fibers becomes a factorof increasing importance. The critical temperature" referred to hereinis defined as the temperature at which the fibrous configuration of agiven sample of acrylic fibrous starting material will be destroyed inthe absence of prior stabilization.

In a preferred embodiment of the invention the acrylic starting materialexhibits a critical temperature of at least about 300C, e.g. about 300to 330C. In addition to visual observation, the detection of thecritical temperature of a given acrylic fibrous material may be aided bythe use of thermoanalytical methods, such as differential scanningcalorimeter techniques, whereby the location and magnitude of theexethermic reaction can be measured quantitatively.

The stabilized acrylic warp ends l retain essentially the same fibrousconfiguration as the starting material, (2) are capable of undergoingcarbonization, (3) are black in appearance, (4) are non-burning whensubjected to an ordinary match flame, and (5) commonly contain a boundoxygen content of at least about 7 percent by weight as determined bythe Unterzaucher analysis.

In a preferred embodiment of the process the sateen tape (heretoforedescribed) is stabilized in accordance with the processing conditions ofcommonly assigned U.S. Ser. Nos. 749,957, filed Aug. 8, 1968, and865,332, filed Oct. 10, 1969 (now abandoned) which are hereinincorporated by reference.

The carbonization heating zone is commonly provided with an inert ornon-oxidizing atmosphere at a temperature of at least about 900C. (e.g.900 to l,600C. Suitable inert atmospheres include nitrogen, argon,helium, etc. During the carbonization reaction elements present in thecontinuous length of fibrous material other than carbon, e.g. nitrogen,hydrogen and oxygen are substantially expelled until the warp endscontain at least 90 per cent carbon by weight, and preferably at least95 per cent carbon by weight.

An optional graphitization zone is commonly provided with an inert ornon-oxidizing atmosphere at a more highly elevated temperature of about2,000 to 3,lC.

A longitudinal tension may optionally be applied to the tape whilepassing through the carbonization and- /or graphitization heating zonesin accordance with techniques known in the art.

ln a preferred embodiment of the process the carbonization andgraphitization of a stabilized acrylic sateen tape may be conducted bythe continuous passage of the same through a single heating apparatus,such as the susceptor of an induction furnace, provided with atemperature gradient in accordance with the teachings of commonlyassigned U.S. Ser. No. 777,275, filed Nov. 20, 1968 (now abandoned),which is herein incorporated by reference. A partially preferredsusceptor for use in the production of carbonaceous fibrous materialswhile in tape form is disclosed in commonly assigned U.S. Ser. No.46,675, filed June 16, 1970 (now U.S. Pat. No. 3,656,910), which isherein incorporated by reference.

The carbonaceous tape, whether formed of amorphous or graphitic carbon,can next optionally be passed through a surface treatment zone whereinits ability to bond to a matrix material is enhanced. Any conventionalsurface treatment technique may be selected. Additionally, the tape(preferably following surface treatment) can optionally be passedthrough a coating zone wherein it is impregnated with a resinousmatrix-forming material, e.g. an epoxy resin.

During the stabilization and carbonization steps of the present processit is common for the width of the tape to diminish due to controlledshrinkage as elements other than carbon are expelled. A flat tapeconfiguration is nevertheless retained.

The tape undergoing treatment in the present process is continuouslypassed in the direction of its length through each of the heating zones(e.g. a stabilization zone and a carbonization zone). If desired, theforward movement of the tape may be terminated between heating zones andthe tape collected upon a support where it is stored prior to additionalprocessing. it is recommended, however, that the heating zones bealigned in close proximity and the tape continuously passed from onezone to another without termination of the forward movement. Variousrolls, or other guides may be employed to direct the movement of thetape as will be apparent to those skilled in fiber technology.

The following examples are provided as specific illustrations of theinvention. It should be understood, however, that the invention is notlimited to the specific details set forth in the examples.

In the examples tapes of various sateen weave constructions inaccordance with the present invention were continuously passed in thedirection of their length through l a pretreatment zone, (2) astabilization zone, (3) a heating zone provided with a temperaturegradient wherein both carbonization and graphitization were carried out,(4) and a surface treatment zone. Following resin impregnation compositearticles incorporating the resulting graphite tape as fibrousreinforcement were formed.

Each tape was produced by initially beaming 200 warp ends of a dry spunacrylonitrile homopolymer,

and inserting a weft pick by useof a Fletcher narrow fabric loom. Eachwarp end consisted of about 385 continuous filaments having a totaldenier of about 775, and was provided with a twist of about 0.5 turn perinch. The 200 warp ends were aligned in adjoining parallel contact toform a flat tape having a width of 4 inches.- Prior to incorporation inthe tape the warp ends had been hot drawn to a single filament tenacityof about 4 grams per denier.

The pretreatment of the acrylonitrile homopolymer tape was conducted inaccordance with the teachings of commonly assigned U.S. Ser. No. 17,962,filed Mar. 9, 1970 (now abandoned). The tape was continuously passedthrough an oven containing circulating air provided at about 220C. whileunder a longitudinal tension sufficient to permit a 16 per centreduction in length brought about by shrinkage for a residence time ofabout 300 seconds. The stabilization (i.e. preoxidation) was conductedin accordance with the teachings of commonly assigned U.S. Ser. No.865,332, filed Oct. 10, 1969 (now abandoned). The tape was continuouslypassed through an oven containing circulating air maintained at about265C. while under a longitudinal tension sufficient to maintain aconstant length for a residence time of about 175 minutes. Thepreoxidized tape was black in appearance, retained its initial fibrousconfiguration essentially intact, was non-burning when subjected to anordinary match flame, and contained'a bound oxygen content of K0 percentbyweight as determined by the Unterzaucher analysis.

The preoxidized tape was continuously passed through a heating zone ofan induction furnace provided with a nitrogen atmosphere and atemperature gradient in accordance with the teachings of commonlyassigned U.S. Ser. No. 777,275, filed Nov. 20, 1968 (now abandoned). Thehollow graphite susceptor of the induction furnace was formed inaccordance'with the teachings of commonly assigned U.S. Ser. No. 46,675,filed June 16, 1970 (now U.S. Pat. No. 3,656,910). The temperaturegradient within the heating zone raised the tape from room temperature(i.e. about 25C.) to a temperature of 800C. in approximately 50 secondsafter entering the susceptor, from 800 to l,600C. in approximately 25seconds to produce a carbonized tape, and from l,600 to 2,750C. in

approximately 50 seconds where it was maintained i50C for about 40seconds to produce a graphitized tape. A longitudinal tension of pounds(i.e. about molecular oxygen in an inert carriergas. The surface treatedtape was collected by winding upon a package.

Tensile and interlaminar shear strength test bars were formed employingthe surface treated tape as a fibrous reinforcing medium in a resinousmatrix. The tensile test bars had dimensions of 8.5 inches x 0.5 inch X0.03 inch, and the interlaminar shear strength test bars had dimensionsof 8 inches X 0.25 inch X 0.125 inch. The composite articles were formedby immersing strips of the tape in a liquid epoxy resin-hardener mixtureprovided at about 70C., removing excess resin, placing a plurality ofthe strips of the impregnated tape in a fixed stop matched die mold, andcuring for 40 minutes at 93C. with minimal pressure, 80 minutes at 93C.at a pressure of I psi, and 150 minutes at 200C. at a pressure of 100psi, cooling the resulting bars to room temperature, trimming the same,and cementing tabs to the ends of the bars for use in an Instron tester.Twelve plies of the tape were utilized in the tensile test bars, and 24plies of the tape were utilized in the interlaminar shear strength testbars. The resinous matrix material used in the formation of thecomposites was provided as a solventless system which contained I00parts by weight epoxy resin and 88 parts by weight of anhydride curingagent.

The tensile strength and the horizontal interlaminar shear strength ofthe resulting composites were determined. The tensile strength wasdetermined employing a modified ASTM D638 procedure utilizing fiberglasstabs to avoid clamp damage. Precise alignment of the bars was obtainedprior to setting the clamps. The horizontal interlaminar shear strengthof the composite was determined by short beam testing of the fiberreinforced composite according to the procedure of ASTM D2344-65T asmodified for straight bar testing with a 4:1 span to depth ratio.

EXAMPLE I The acrylonitrile homopolymer tape having; a double faced 4float filling sateen weave construction as illustrated in FIG. 1 wasemployed. Representative warp ends are identified at A andrepresentative weft picks at B. The weft pick was formed fromapproximately 200 continuous fils of acrylonitrile homopolymer having atotal denier of about 400 and a twist of 4.5 turns per inch. The weftpick was provided at a frequency of 4 picks per inch of tape.

The counter for the weave was one. The weave pattern for the tape isillustrated in FIG. 2. The appearance of a number within a box of theweave pattern indicates that the corresponding warp end is present uponthe surface of the woven tape. The absence of a number within a box ofthe weave pattern indicates that a weft pick is present upon the surfaceof the woven tape. A plain weave construction was employed when the weftpick traversed the pair of warp ends adjacent each edge of the tape.

Following stabilization (i.e. preoxidation) the tape width had decreasedto 2.8 inches. Following carbonization and graphitization the width ofthe tape had decreased to 2.4 inches. The average single filamenttensile properties (20 breaks tested) of the warp ends followinggraphitization and prior to surface treatment were 10 grams per deniertenacity, and 3,250 grams per denier Youngs modulus. The resultingcomposites exhibited an average tensile strength of 70,000 psi, and anaverage horizontal interlaminar shear strength of 7,300

psi.

EXAMPLE II The acrylonitrile homopolymer tape having a double faced 8float filling sateen weave construction as illustrated in FIG. 3 wasemployed. Representative warp ends are identified at A andrepresentative weft picks at B. The weft pick was formed fromapproximately I00 continuous fils of acrylonitrile homopolyrner having atotal denier of about 200 and a twist of 0.5 turn per inch. The weftpick was provided at a frequence of 2 picks per inch of tape.

The counter for the weave was one. The weave pattern for the tape isillustrated in FIG. 4. The appearance ofa number within a box of theweave pattern indicates that the corresponding warp end is a presentupon the surface of the woven tape. The absence of a number within thebox of the weave pattern indicates that a weft pick is present upon thesurface of the woven tape. A plain weave construction was employed whenthe weft pick traversed the pair of warp ends adjacent each edge of thetape.

Following stabilization (i.e. preoxidation) the tape width had decreasedto approximately 2.9 inches. Following carbonization and graphitizationthe width of the tape had decreased to approximately 2.5 inches. Theaverage single filament tensile properties (20 breaks tested) of thewarp ends following graphitization and prior to surface treatment were10.2 grams per denier tenacity, and 3,200 grams per denier Youngsmodulus. The resulting composites exhibited an average tensile strengthof 95,000 psi, and an average horizontal interlaminar shear strength of8,700 psi.

EXAMPLE III The acrylonitrile homopolymer tape having a double faced 8float filling sateen weave construction similar to that illustrated inFIG. 3 was employed. The weft pick was formed from approximately 200continuous fils of acrylonitrile homopolymer having a total denier ofabout 400 and a twist of 4.5 turns per inch. The weft pick was providedat a frequency of 6 picks per inch of tape.

The counter for the weave was one. The weave pattern for the tape isillustrated in FIG. 4. The appearance of a number within a box of theweave pattern indicates that the corresponding warp end is present uponthe surface of the woven tape. The absence of a number within a box ofthe weave pattern indicates that a weft pick is present upon the surfaceof the woven tape. A plain weave construction was employed when the weftpick traversed the pair of warp ends adjacent each edge of the tape.

Following stabilization (Le. preoxidation) the tape width had decreasedto 2.9 inches. Following carbonization and graphitization the width ofthe tape had decreased to 2.5 inches. The average single filamenttensile properties (20 breaks tested) of the warp ends followinggraphitization and prior to surface treatment were 10 grams per deniertenacity, and 3,000 grams per denier Youngs modulus. The resultingcomposite exib-, ited an average tensile strength of 72,000 psi, and anaverage horizontal interlaminar shear strength of 7,700 psi. Acomparison of the composite properties indicates that the tape ofExample II is preferred to that of Example III for utilization in theprocess of the invention.

EXAMPLE IV The acrylonitrile homopolymer tape having a double faced l6float filling sateeen weave construction as illustrated in FIG. wasemployed. Representative warp ends are identified at A andrepresentative weft picks at B. The weft pick was formed fromapproximately 100 continuous fils of acrylonitrile homopolymer having atotal denier of about 200 and a twist of 0.5 turn per inch. The weftpick was provided at a frequency of 4 picks per inch of tape.

The counter for the weave was one. The weave pattern for the tape isillustrated in FIG. 6. The appearance of a number within a box of theweave pattern in-' dicates that the corresponding warp end is presentupon the surface of the woven tape. The absence of a number within a boxof the weave pattern indicates that a weft pick is present upon thesurface of the woven tape. A plain weave construction was employed whenthe weft pick traversed the pair of warp ends adjacent each edge of thetape.

Following stabilization (i.e. preoxidation) the tapewidth had decreasedto approximately 2.9 inches. Following carbonization and graphitizationthe width of the tape had decreased to approximately 2.5 inches. Theaverage single filament tensile properties (20 breaks tested) of thewarp ends following graphitization and prior to surface treatment were10 grams per denier tenacity, and 3,309 grams per denier Youngs modulus.The resulting composites exhibited an average tensile strength of105,000 psi, and an average horizontal interlaminar shear strength of8,400 psi.

For comparative purposes an acrylonitrile homopolymer tape employingidentical warp ends was processed as heretofore described in the absenceof any form of weaving. More specifically, the warp ends were maintainedin parallel in the form ofa flat tape which lacked a weft pickinterlaced therewith. The average single filament tensile propertiesbreaks tested) of the warp ends following graphitization and prior tosurface treat ment were l 1.5 grams per denier tenacity, and3,200 gramsper denier Youngs modulus. The resulting cornposites exhibited anaverage tensile strength of 90,000 psi. and an average horizontalinterlaminar shear strength of 8.800 psi. A comparison of the compositeproperties indicates that the presence of the weft pick withincomposites reinforced by carbonized sateen tapes formed in accordancewith the present process results in no substantial diminution ofcomposite properties. Additionally, the present process offerssignificant fiber handling advantages.

For comparative purposes a woven acrylonitrile homopolymer tape wasformed in a plain weave construction and processed as heretoforedescribed. The warp ends were in adjoining contact throughout theprocess.

The weave construction is illustrated in FIG. 7. Repretive weft picks atB. The weft pick was formed from approximately 200 continuous fils ofacrylonitrile homopolymer having a total denier of about 400 and a twistof 4.5 turns per inch. The weft pick was provided at a frequency of 2picks per inch of tape. The counter for the weave was one. The weavepattern for the tape is illustrated in FIG. 8. The appearance of anumber within a box of the weave pattern indicates that thecorresponding warp end is present upon the surface of the woven tape.The absence of a number within a box of the weave pattern indicates thata weft pick is present upon the surface of the woven tape. Followingstabilization (i.e. preoxidation) the tape width had decreased to 3.15inches. Following carbonization and graphitization the width of the tapehad decreased to 2.4 inches. The average single filament tensileproperties (20 breaks tested) of the warp ends following graphitizationand prior to surface treatment were 8.6 grams per denier tenacity, and3,300 grams per denier Youngs modulus. The resulting composite exhibitedan average tensile strength of 46,000 psi, and an average horizontalinterlaminar shear strength of 7,200 psi. A comparison of compositeproperties indicates a substantial diminution of composite propertiesresults when the reinforcing tape is formed in the plain weaveconstruction.

Although the invention has been described with preferred embodiments, itis to be understood that variations and modifications may be resorted toas will be apparent'to those skilled in the art. Such variations andmodificationsare to be considered within the purview and scope of theclaims appended hereto.

We claim:

ll. In a process for the simultaneous conversion of a plurality ofadjoining ends of a multifilament acrylic fibrous material capable ofundergoing conversion to a carbonaceous fibrous material selected fromthe group consisting essentially of an acrylonitrile homopolymer and anacrylonitrile copolymer containing at least about 85 mol per cent ofacrylonitrile units and up'to about 15 mol per cent of one or moremonovinyl units copolymerized therewith, while in the form ofa tape to acarbonaceous fibrous material wherein said ends are continuously passedin the direction of their length through a series of heating zones whilesubstantially suspended therein to form a fibrous product which containsat least 90per cent carbon by weight, the improvement which comprisesproviding said fibrous material during at least the stabilizationportion of the said conversion process in the form of a tape of sateenweave construction consisting of at least 32 adjoining substantiallyparallel linear multifilament warp ends of fibrous material essentiallycoextensive with the length of said tape and a weft pick which initiallyis provided prior to stabilization as a multifilament acrylic yarnhaving a total denier below about 400 interlaced therewith at aplurality of points capable of maintaining and substantially parallelrelationship of said warp ends which substantially floats at least 4 ofsaid warp ends 2. An improved process according to claim 1 wherein saidwarp ends are an acrylonitrile homopolymer.

3. An improved process according to claim 1 wherein the composition ofsaid weft pick is substantially identical to that of said warp ends.

4. An improved process according to claim 1 wherein said fibrousmaterial is provided in the form of said tape of sateen I weaveconstruction while being passed through a stabilization zone and acarbonization zone.

hibiting a twist of about 0.1 to 5 turns per inch.

8. An improved process according to claim 7 wherein said weft pickpossesses a twist of about 0.5 turn per inch.

9. An improved process according to claim 1 wherein said tape of sateenweave construction includes 32 to 500 adjoining substantially parallellinear warp ends.

10. An improved process according to claim I wherein the total denier ofsaid weft pick is equal to or less than that of each of said warp ends.

11. An improved process according to claim 1 wherein said weft pickpossesses a twist of about 0.1 to 3 turns per inch.

12. An improved process according to claim 1 wherein said weft picksubstantially floats from about 4 to 16 of said warp ends prior to eachadditional interlacing point in the main body of said tape as said warpends are traversed.

13. An improved process according to claim 1 wherein said weft pick isprovided at a frequency of about 1 to 3 picks per inch of said tape.

2. An improved process according to claim 1 wherein said warp ends arean acrylonitrile homopolymer.
 3. An improved process according to claim1 wherein the composition of said weft pick is substantially identicalto that of said warp ends.
 4. An improved process according to claim 1wherein said fibrous material is provided in the form of said tape ofsateen weave construction while being passed through a stabilizationzone and a carbonization zone.
 5. An improved process according to claim1 wherein said fibrous material is provided in the form of said tape ofsateen weave construction while being passed through a stabilizationzone, a carbonization zone, and a graphitization zone.
 6. An improvedprocess according to claim 1 wherein said fibrous material is providedin the form of said tape of sateen weave construction while being passedthrough a stabilization zone, a carbonization zone, and a surfacetreatment zone.
 7. An improved process according to claim 1 wherein saidwarp ends are continuous multifilament yarns exhibiting a twist of about0.1 to 5 turns per inch.
 8. An improved process according to claim 7wherein said weft pick possesses a twist of about 0.5 turn per inch. 9.An improved process according to claim 1 wherein said tape of sateenWeave construction includes 32 to 500 adjoining substantially parallellinear warp ends.
 10. An improved process according to claim 1 whereinthe total denier of said weft pick is equal to or less than that of eachof said warp ends.
 11. An improved process according to claim 1 whereinsaid weft pick possesses a twist of about 0.1 to 3 turns per inch. 12.An improved process according to claim 1 wherein said weft picksubstantially floats from about 4 to 16 of said warp ends prior to eachadditional interlacing point in the main body of said tape as said warpends are traversed.
 13. An improved process according to claim 1 whereinsaid weft pick is provided at a frequency of about 1 to 3 picks per inchof said tape.